This acceleration detector (10) has a direction-vector setting unit (11) that sets a direction vector (u) on the basis of detection declinations (a, b) that define a target detection direction in an orthogonal coordinate system using three mutually orthogonal axes (x, y, and z) and an inner-product calculation unit (12) that obtains a detected acceleration signal (v(n)) by calculating the inner product between the aforementioned direction vector (u) and observed acceleration signals (x(n), y(n), z(n)) for the respective axes of the aforementioned orthogonal coordinate system.